<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      Math.random() * (3 - 1) + 1;		  //  1 ≤ 返回结果 < 3
      Math.random() * (20 - 10) + 10;		// 10 ≤ 返回结果 < 20
      Math.random() * (99 - 88) + 88;		// 88 ≤ 返回结果 < 99
    </script>
  </body>
</html>